OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 1
WEEK-2
Topics: Virtualization
technology, working, types, Potentials and challenges of Virtualization, Virtual
Machines, Containers.
Linux Boot process. Linux command line - Interpreter, shell,
CLI over GUI,
Types of user’s super
and normal, Linux user manual.
Virtualization technology
Virtualization is technology that allows you to create multiple simulated environments or dedicated
resources from a single, physical hardware
system. Software called
a hypervisor
connects directly to that
hardware and allows you to split 1 system into
separate, distinct, and secure
environments known as virtual
machines (VMs). These VMs rely on the
hypervisor’s ability to separate the
machine’s resources from the
hardware and distribute them appropriately.
The physical hardware, equipped with a hypervisor, is called the host,
while the many VMs that use its
resources are guests. These guests
treat computing resources—like CPU, memory, and storage—as a pool
of resources that can easily be relocated.
Benefits of Virtualization
Partitioning: Multiple applications and operating
systems can be supported within a single physical
system Servers can be consolidated into
virtual machines on either a
scale-up or
scale-out
architecture Computing resources are treated as a uniform pool to be allocated to virtual machines in
a controlled manner
Isolation:
Virtual machines are completely
isolated from the host machine
and other virtual
machines. If a virtual machine crashes, all
others are unaffected Data does
not leak across
virtual
machines and applications can only communicate
over configured network connections.
Encapsulation: Complete
virtual machine environment is saved as a single file; easy to back up,
move and copy Standardized
virtualized hardware is presented to the
application -
guaranteeing
compatibility.
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 2
The Challenges Of Virtualization
Performance
Monitoring: Unlike
physical servers, monitoring the
performance of the virtual servers
requires a different approach.
Conventional CPU and memory utilization monitoring don’t work. In a
virtual infrastructure, the VMs share the common hardware resources such as CPU, memory,
and storage.
Metrics such as CPU ready, memory ready, memory balloon, and swapped memory have to be monitored
across all the VMs.
Security: In virtualized systems, the hypervisor is the single point
of failure in
security and if you lose it,
you lose the
protection of sensitive information. So the best way to
avoid hyper-jacking is to use hardware-
rooted trust and secure launching of the
hypervisor.
Managing VM Sprawl: The virtual infrastructure has to be monitored continuously to identify VMs
that
are idle for a certain period, VMs that
have resources
overprovisioned or under-provisioned, and VMs that
are not even powered on
since they were provisioned.
By removing such unused VMs – or optimizing the
resources allocated to VMs – virtual sprawl can be greatly minimized.
Attacks on Virtualization features: Although there are
multiple features
of virtualization that can be
targeted for exploitation, the more common targets include VM migration and virtual networking functions.
VM migration, if done insecurely, can expose all aspects of a given VM to both passive
sniffing and active
manipulation attacks.
Compliance and Management Challenges: Compliance auditing and enforcement, as well as day-to-day
system management, are challenging issues when dealing with virtualized systems. VM sprawl will make it
a challenge to get accurate results from
vulnerability assessments.
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 3
Capacity Planning: Without proper capacity planning,
the server management team will have a
hard time
scaling the infrastructure to meet business demands. Capacity planning also requires constant
monitoring of
the virtual infrastructure. Plan how many
resources have to be added to handle the future load.
Licensing Issues:
Software vendors license virtualization in different ways.
For example, one organization
was running seven virtual instances on a server with four physical
cores. Depending on which software they
were using, they required seven licenses from one vendor – but only four from another.
How does virtualization works:
Software called hypervisors
separate the physical
resources from the
virtual environments—the
things that need those resources. Hypervisors can sit on top of an operating system (like on a laptop) or be
installed directly
onto hardware
(like a server),
which is how most enterprises
virtualize. Hypervisors take
your physical resources and divide them up so
that virtual environments can use them.
Resources are partitioned
as needed from the physical
environment to the many virtual
environments. Users
interact with and
run computations within the virtual
environment (typically called a
guest machine or virtual machine).
The virtual machine functions as
a single data file. And like any digital
file, it can be moved from one computer to
another, opened in either one, and be expected to work the same.
When the virtual environment is running and a user or program issues an instruction that
requires
additional resources from the physical environment, the hypervisor relays the request to the physical system
and caches the changes—which
all happens at
close to native
speed (particularly if the
request is sent
through an open source hypervisor based on KVM, the Kernel-based Virtual Machine)
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 4
Types of Virtualization
Data Virtualization
Data that’s spread
all over can be
consolidated into a single source. Data virtualization allows companies to
treat data as a
dynamic supply—providing processing
capabilities that can bring together data
from multiple
sources, easily accommodate new
data sources,
and transform data according to user
needs. Data
virtualization tools
sit in front of multiple data
sources and
allows them to
be treated as single source,
delivering the needed data—in the required form—at the right time to any
application or user.
Desktop virtualization
Easily confused with operating system virtualization—which allows you to deploy multiple operating
systems on a single machine—desktop
virtualization allows a central
administrator (or automated
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 5
administration tool)
to deploy simulated desktop
environments to hundreds of physical machines
at once.
Unlike traditional
desktop environments that are
physically installed, configured, and
updated on
each
machine, desktop virtualization allows admins to perform mass configurations, updates, and security checks
on all virtual desktops.
Server virtualization
Servers are computers
designed to process a high volume of specific tasks really well so other computers—
like laptops and desktops—can
do a variety of other tasks.
Virtualizing a
server lets it to do more of those
specific functions and involves
partitioning it so
that the components
can be used
to serve multiple
functions.
Operating system virtualization
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 6
Operating system virtualization
happens at the
kernel—the central task managers of
operating systems. It’s
a useful way to run
Linux and
Windows environments side-by-side.
Enterprises can also
push virtual
operating systems to computers, which:
Reduces bulk
hardware costs, since
the computers don’t require
such high out-of-the-box
capabilities.
Increases security, since all virtual instances can be monitored and isolated.
Limits time spent on IT services like
software updates.
Network functions virtualization
Network functions
virtualization (NFV) separates a network's key
functions (like
directory services, file
sharing, and IP configuration)
so they can be distributed among environments. Once software functions are
independent of the
physical machines they once lived on, specific functions can be packaged together into a
new network and assigned to an environment.
Virtualizing networks reduces the number of physical
components—like switches, routers,
servers, cables, and hubs—that are needed to
create multiple,
independent networks, and it’s particularly
popular in the telecommunications industry.
Virtual Machines
A
Virtual Machine is the representation of a physical machine by software.
It has its
own set of
virtual hardware (e.g., RAM, CPU,
NIC, hard disks,
etc.) upon which
an operating system and applications
are loaded. The operating
system sees a consistent, normalized set of
hardware regardless
of the actual
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 7
physical hardware
components. Software called
a hypervisor separates the machine’s resources from
the
hardware and provisions them appropriately so
they can be used by the VM
Virtual Machines are not
emulators are simulators. They are real machines that can
do the same
things physical computers
can do and more. Because of the flexibility of
virtual machines, physical
machines become less a way to provide services (application, databases etc.)
and more a way to house the
virtual machines that provide those
resources. Servers are easy to manage if they are on virtual machines.
Virtual machines also reduce cost of hardware,
maintenance and environment support.
Containers
Linux containers and
virtual machines (VMs) are packaged computing
environments that combine
various IT components and isolate them from the rest of the system. Their main
differences are in
terms of
scale and portability.
Containers are typically measured by the megabyte. They don’t package anything bigger than an app
and all the files necessary
to run, and are often used to package
single functions
that perform specific tasks
(known as a microservice). The lightweight nature of
containers—and their shared operating system
(OS)—
makes them very easy to move across multiple
environments.
VMs are typically measured by the
gigabyte. They usually contain their own OS, allowing them to
perform multiple
resource-intensive functions at once. The
increased
resources available to VMs allow
them to abstract, split, duplicate, and emulate
entire servers, OSs, desktops, databases, and networks.
Linux boot process
The following are the 6 high level stages of a
typical Linux boot process.
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 8
1. BIOS
BIOS stands for Basic Input/Output System
Performs some system integrity checks
BIOS loads and executes the MBR boot
loader.
2. MBR
MBR stands for Master Boot Record.
It is located in the 1st sector of the
bootable disk. Typically /dev/hda, or /dev/sda
MBR is less than 512 bytes in size. This
has three components
1) primary boot loader info in 1st 446
bytes
2) partition table info in next 64 bytes
3) MBR validation check in last 2 bytes.
It contains information about GRUB (or
LILO in old systems).
So, in simple terms MBR loads and
executes the GRUB boot loader.
3. GRUB
GRUB stands for Grand Unified Bootloader.
If you have multiple
kernel images installed
on your system,
you
can choose which one to
be
executed.
GRUB displays
a splash screen,
waits for few seconds,
if you don’t enter anything, it loads
the
default kernel image as specified in the grub
configuration file.
GRUB has the knowledge
of the filesystem (the
older Linux
loader LILO didn’t understand
filesystem).
Grub configuration file is /boot/grub/grub.conf (/etc/grub.conf is a link
to this). The following is
sample grub.conf of CentOS.
4. Kernel
Mounts the root file system as specified
in the “root=” in grub.conf
Kernel executes the /sbin/init program
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 9
Since init was
the 1st program to be executed
by Linux Kernel, it has the process id (PID) of 1. Do a
‘ps -ef | grep init’
and check the pid.
initrd stands for Initial RAM Disk.
initrd is used
by kernel as temporary root file system until kernel is booted and the real root file
system is mounted. It also
contains necessary
drivers compiled
inside, which helps it to access the
hard drive partitions, and other hardware.
5. Init
Looks at the /etc/inittab file to decide
the Linux run level.
Following are the available run levels
0 – halt
1 – Single user
mode
2 – Multiuser, without NFS
3 – Full
multiuser mode
4 – unused
5 – X11
6 – reboot
Init identifies the default initlevel
from /etc/inittab and uses that to load all appropriate program.
Execute ‘grep initdefault /etc/inittab’
on your system to identify the default run level
If you want to get
into trouble, you can set
the default run level to
0 or 6.
Since you
know what 0
and 6 means, probably you might not do that.
Typically, you would set the default run
level to either 3 or 5.
6. Runlevel programs
When the Linux system is booting up, you
might see various services getting
started. For example, it
might say “starting sendmail
…. OK”. Those
are the runlevel programs, executed from the run level
directory as defined by your run level.
Depending on
your default init level setting, the system
will execute the programs from one of
the
run level (0 to 6) directories
(/etc/rc.d/rc{0-6}.d/)
Under the /etc/rc.d/rc*.d/ directories,
you would see programs that start with S and K.
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 10
Programs starts with S are used during
startup. S for startup.
Programs starts with K are used during
shutdown. K for kill.
That is what happens during the Linux boot
process.
Linux command line
The Linux command line is
a text
interface to your computer.
Also known as
shell, terminal,
console,
command prompts and many others, is a computer program intended to interpret commands.
Allows users to execute commands
by manually typing at the terminal, or has the ability to automatically
execute commands which were programmed in “Shell
Scripts”.
First look at the command line
When a terminal is open, it presents you with a
prompt.
Let's analyze the
screenshot above:
Line 1: The shell prompt, it
is composed by username@hostname:location$
Username: our username is
called “john”
Hostname: The name of the system we are
logged on
Location: the working directory we are in
$: Delimits the end of prompt
After the $ sign, we can type a command and press Enter for this command to be executed.
Line 2: After the prompt, we have typed the command whoami
which stands for “who am i“ and pressed
[Enter] on the keyboard.
Line 3: Shows us the result of the
whoami command we have previously issued, also
known as command
output. This command simply prints out the
username of the current user.
Line 4: Shows an example of
another basic command called pwd which stands for print working
directory.
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 11
Line 5: As seen before, this line shows
the result of
the command previously issued. /tmp is
our working
directory.
Line 6: Presents us with a new
prompt, and waits for us to type a new command.
There are a few important things to keep in mind
when using a Linux shell:
It is case sensitive
The / (forward-slash) is a special
character used as directory separator
Nearly every Linux command supports --help argument
File extensions don’t matter
Common Types of Shells in Linux
1.
The Bourne Shell (sh -
# and $) was originally developed in 1979 by Stephen Bourne while working
at Bell Labs.
2.
The GNU Bourne Again Shell (bash – bash-versionnumber# and bash-versionnumber$) was written
as a free and open source replacement for the
Bourne Shell.
3.
The C Shell (csh – hostname# and hostname$) was created at university of California by Bill Joy to
include useful programming features.
4.
The Korn Shell (ksh - #
and $) was developed at AT & T Bell Labs
by David Korn, to improve the
Bourne Shell.
All the above shells are stored in Linux
Directories - /bin/sh, /bin/bash, /bin/csh and /bin/ksh respectively.
To check your present login shell, use the below
command
To check the available shells in the system
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 12
Linux user types
There are two types of users – the
root or super user and normal users.
A root or
super user can access all the files, while the normal user has
limited access to files. In
computing, the superuser is a special user account used for system administration. Depending on the
operating system
(OS), the actual
name of this
account might
be root,
administrator, admin or
supervisor.
Normal users
are the users created
by the root
or another user with sudo
privileges. Usually, a
normal user has a real login shell and a home directory. Each user has a numeric user ID called UID.
A super user can add, delete and modify a user account. The full
account information
is stored
in
the /etc/passwd file
and a hash password is stored in the file /etc/shadow.
Interpreters: A command line interpreter is any program that
allows the
entering of commands and then
executes those commands to the operating system.
It's literally an interpreter of commands.
CLI over GUI
CLI : Command line Interface, allows the users
to interact with the system using commands.
GUI : Graphical User Interface, allows the users
to interact with the system using graphical elements such
as windows, icons, menus
Sl no
CLI
GUI
1
CLI is difficult to use.
Whereas it is easy to use
2
It consumes low memory.
While consumes more memory
3
In CLI we can obtain high precision.
While in it, low precision is obtained
4
CLI is faster than GUI
The speed of GUI is slower than CLI.
5
CLI’s appearance can not be modified
or changed.
While it’s appearance can be modified or changed.
6
CLI operating system needs only
keyboard.
While GUI operating system need both mouse and
keyboard.
7
In CLI, input is entered only at
command prompt.
While in GUI, input can be entered anywhere on the
screen.
8
In CLI, the information is shown or
presented to the user in plain text and
files
While in GUI, the information is shown or presented
to the user in any form such as: plain text, videos,
images, etc.
9
In CLI, there are no menus provided.
While in GUI, menus are provided.
10
There are no graphics in CLI.
While in GUI, graphics are used.
11
CLI do not use any pointing devices.
While it uses pointing devices for selecting and
choosing items.
12
In CLI, spelling mistakes and typing
errors are not avoided
Whereas in GUI, spelling mistakes and typing errors
are avoided.
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 13
Linux User Manual
man
command
in Linux is used to display the user manual of any command that we can run on the
terminal. It provides a detailed view of the command which includes NAME, SYNOPSIS,
DESCRIPTION, OPTIONS, EXIT STATUS, RETURN VALUES, ERRORS, FILES, VERSIONS,
EXAMPLES, AUTHORS and SEE ALSO.
Every manual is divided into the following sections:
Executable
programs
or shell commands
System calls
(functions provided by
the kernel)
Library
calls (functions within program
libraries
Games
Special
files (usually found
in /dev)
File formats and
conventions eg /etc/passwd
Miscellaneous (including macro packages and
conventions), e.g.
groff(7)
System administration
commands (usually only for root)
Kernel routines
[Non standard]
Syntax :
$man [OPTION]... [COMMAND NAME]...
Example: 1. $ man printf
OSA [20CS42P] By: M.B.A KHAN, Lecturer C.S Dept.
Dept. of Collegiate and Technical Education,
G.P.T Mudhol-587313 Page 14
2. man -f ls
Few Commands to Try!
1.
cat /etc/shells --- To Know
the Valid Login Shells available for the system.
2.
whoami --- To know the
currently logged in user.
3.
pwd --- To know the Present
Working Directory.
4.
su --- To switch user or
substitute {This command needs root password which is locked in Ubuntu}.
5.
sudo –i
--- Alternative to su command to get
privileges of root (administrator).
6.
passwd --- To set or change the password of root.
7.
su username or exit or ctrl+d or logout --- To return to user
account.
